1. Field of the Invention
The present invention relates to an image display device. More specifically, the present invention relates to a stereoscopic image display device and a terminal device capable of displaying stereoscopic images according to the positioning state of the device.
2. Description of the Related Art
Conventionally, there has been introduced a stereoscopic image display device with which stereopsis can be achieved without using eyeglasses by projecting images of different parallax to the left and right eyes of an observer by providing different images towards a plurality of viewpoints.
As a stereoscopic image display method used in such device, known is a method with which image data for each viewpoint are synthesized and displayed on a display unit, and the displayed synthesized image is separated by an optical separation module constituted with a lens or a barrier (a light-shielding plate) having a slit and separated images are provided to each of the viewpoints, i.e., to the left and right eyes of the observer.
As the optical separation module, this method generally employs a parallax barrier constituted with a barrier having a great number of stripe-patterned slits or a lenticular lens in which cylindrical lenses exhibiting the lens effect in one direction are arranged.
Further, there have been proposed various kinds of display devices which employ image distribution modules (also referred to as optical separation modules hereinafter) which are capable of performing optical image separation not only in a first direction that is the normal observing direction but also in a second direction that is orthogonal to the first direction (e.g., Japanese Unexamined Patent Publication 2011-17788 (Patent Document 1); Japanese Unexamined Patent Publication 2011-43623 (Patent Document 2); Japanese Unexamined Patent Publication 2011-69869 (Patent Document 3); Japanese Unexamined Patent Publication 2010-249954 (Patent Document 4); Japanese Unexamined Patent Publication 2011-164637 (Patent Document 5); Japanese Unexamined Patent Publication 2012-215853 (Patent Document 6)). That is, the use of such an image separation module makes it possible to project images of different parallax to the left and right eyes of the observer even when the layout direction of the device is rotated by 90 degrees from the normal observing direction and the display image is changed to fit to that layout, so that the stereoscopic image can be visually recognized from two directions.
In Patent Documents 1 to 3, disclosed is a display device which makes it possible to visually recognize stereoscopic images under two conditions where the layout directions are different by 90 degrees from each other by using an oblique step type, a zigzag type, or a pinhole type parallax barrier as an optical separation module by using generally-used vertically RGB striped rectangular sub-pixels as the base.
Further, Patent Document 4 discloses a display device which makes it possible to visually recognize stereoscopic images in both cases where the layout directions are different by 90 degrees from each other by way of disposing vertical RGB strip rectangular sub-pixels obliquely and using a lens array element as the optical separation module.
Further, Patent Document 5 discloses a display device which makes it possible to visually recognize stereoscopic images in two cases where the layout directions are different by 90 degrees from each other by employing a structure in which pixel matrixes each constituted with same-color pixels arranged in a 2×2 matrix form, for example, are repeatedly arranged in the horizontal direction and the vertical direction in a manner to be of different colors from each other and an optical separation module is provided by corresponding to each of the pixel matrixes.
Further, Patent Document 6 discloses a display device which employs a structure in which sub-pixels are arranged repeatedly in the horizontal direction and the vertical direction in a manner to be in different colors from each other in a pixel constituted with sub-pixels of three colors arranged in a 3×3 matrix form, for example, and a parallax barrier as an optical separation module is provided to each of the pixels in a corresponding manner. Herein disclosed is technical content which makes it possible to visually recognize stereoscopic images in both of the two cases where the layout directions are different by 90 degrees from each other by suppressing generation of crosstalk by decreasing the display area occupying the pixels by providing displays on three sub-pixels out of nine sub-pixels of each pixel, by not providing displays on the other six sub-pixels, and by employing the square-shape sub-pixels. However, with the structures of the display devices disclosed in Patent Documents 1 to 3, there is a layout direction with which the light-ray separating directions separated by the optical separation module becomes parallel to the RGB layout direction. In the layout direction, a so-called “color moiré” occurs, i.e., unevenness in each color when the observer shakes the viewing angle, such that the display quality is greatly deteriorated.
Further, those display devices employ parallax barriers of a great versatility in patterning as the optical separation modules, so that there is an issue of having large deterioration in the transmittance due to loss of light (deterioration in the brightness of the display screen) caused by the light-shielding parts of the parallax barriers. In the meantime, in the case where a lens is employed instead of the parallax barrier to correspond to the layout pattern of the pixels disclosed in Patent Documents 1 to 3, inconveniences result in terms of readiness and cost of manufacture. Therefore, it is not possible to overcome a large issue of deterioration in the transmittance of the parallax barrier.
In the structure of the stereoscopic image display device disclosed in Patent Document 4, there is no layout direction where the direction of light-ray separation done by the optical separation module becomes parallel to the RGB color layout direction. Thus, it is possible to lighten the “color moiré” that is at issue in the technical contents of Patent Documents 1 to 3 described above.
However, pitches of the rectangular sub-pixels of that structure are different in the horizontal direction and the vertical direction. Thereby, color moiré and luminance unevenness occur when the layout direction of the device is changed, so that the 3D resolution and the like vary depending on the layout directions.Further, while the lenticular lens when the long sides of the rectangular sub-pixels are along the horizontal direction is arranged in the vertical direction, the lenticular lens when the long sides of the rectangular sub-pixels are in the vertical direction is arranged by being tilted with respect to the vertical direction. Thus, a sense of jaggies (serration) in increased, due to the oblique lens.
In the structure of the stereoscopic image display device disclosed in Patent Document 5, there is also no layout direction where the direction of light-ray separation done by the optical separation module becomes parallel to the RGB color layout direction. Thus, it is also possible to lighten the “color moiré”.
However, the resolution in the vertical direction becomes half the resolution in the horizontal direction. Because of that, degrees of resolution in the vertical and lateral directions become inconsistent.
In the structure of the stereoscopic image display device disclosed in Patent Document 6, there is also no layout direction where the direction of light-ray separation done by the optical separation module becomes parallel to the RGB color layout direction. Thus, it is also possible to lighten the “color moiré”.
However, in addition to the fact that it is necessary to use two pixels for achieving stereoscopic display, the number of sub-pixels contributed to the display among the number of sub-pixels constituting each pixel is ⅓ to ¼ that is a reciprocal of the number of primary colors. Thus, not only the 3D display resolution is deteriorated but also the power consumption is increased due to the low use efficiency of the sub-pixels and due to the deterioration in the transmittance caused by light loss caused by the barrier.
It is therefore an exemplary object of the present invention to improve the inconveniences of the above-described conventional cases and, more specifically, to provide a stereoscopic image display device, a stereoscopic image display method, and a program therefore capable of displaying significant stereoscopic images with no difference in the degree of resolution in the vertical and lateral directions and having almost no deterioration in the transmittance regardless of the positioning state of the device.